(1) Field of the Invention
This invention relates to bus bars and particularly to miniature bus bars characterized by a high capacitance. More especially, this invention relates to the manufacture of bus bars which incorporate multilayer capacitive elements between pairs of elongated parallel bus conductors. Accordingly, the general objects of the present invention are to provide novel and improved articles and methods of such character.
(2) Description of the Prior Art
Conventional bus bars of relatively small or miniature size have been known in the art for a number of years. Such bus bar devices are used for power and/or signal distribution in many systems, such as, for example, computer back panels and integrated circuit systems. Such prior art multilayer bus bars comprise at least two conductive plates (usually in the form of elongated strips or bars of copper) separated by an insulating film. A typical prior art bus bar of this type may use copper conductors having a thickness of about 10 mils, and the overall dimensions of the bus bar may be from about 0.019 to 0.120 inch thick, from about 0.150 to 0.200 inch wide and range in length up to about 16 inches. Typically, the separating insulating layer is a plastic dielectric film such as the polyester material known as MYLAR. The MYLAR separator layer and the conductive plates are bonded together by an adhesive. Conventional prior art bus bars of this type have relatively low capacitance which results in the devices being comparatively ineffective in attenuating high frequency noise. This high frequency noise is highly undesirable, especially when the bus bar is used for signal distribution.
One prior art approach to eliminating this noise problem involves connecting capacitors to the bus bar after the completion of the bus bar assembly. While this approach raised the capacitance and minimized the noise, it resulted in additional expense and time in manufacturing.
Another type of bus bar structure disclosed in the prior art involves disposing discrete high capacitive elements between a pair of conductors. These bus bars have the desired high capacitance. Examples of such high capacitance bus bars are disclosed in U.S. Pat. Nos. 4,236,038 and 4,236,046 and in patent application Ser. No. 950,266, filed Oct. 10, 1978, now U.S. Pat. No. 4,266,901, all of which are owned by the assignee of the present invention. The high capacitive elements utilized in those inventions are thin layers or chips of dielectric material, usually a ceramic with a high dielectric constant. The opposing surfaces of the chips are typically coated with a thin, integral and continuous film of conductive material and these conductive films are electrically connected to respective ones of the bus conductors.